Unfortunately, the wind had shifted to an east-to-west direction during the disaster. Starting at the Fukushima beach, a swath of farmland running northeast about six miles wide by 25 miles long, washed of human habitation by the tsunami, may be too contaminated by fission product fallout to be repopulated immediately. It may be turned into a nature preserve. Every time it rains at Fukushima I, more radioactive dust is washed down to the shore and out into the ocean, causing issues for Japan’s sizable fishing industry.
None of the spent fuel at Fukushima I, in cooling pools or dry storage, was damaged and no fission products from it leaked into the environment. All of the radioactive contamination was from damaged, hot fuel exposed to steam, which was allowed to escape from Mark I containment structures, stressed beyond the imaginations of the engineers who had designed them. No one had considered that a reactor coming down off full power could be denied electricity for more than a few minutes, given the multi-level, parallel-redundant systems built to prevent it. After Unit 1 blew up, refilling the condensate tanks from external sources and wiring up emergency generators was delayed, and the remaining reactors fell like dominoes. Without an ultimate heat sink, the core structure in a nuclear reactor that has recently generated a billion watts of power will eventually melt from the delayed energy release in the fuel. If the workers had been able to refill the condensate tanks in Units 2 and 3, there would have been a lot of steam, but the vapor would not have contained any dissolved fuel, and it would not have been radioactive. With externally provided water and electricity, Units 2 and 3 would have survived.[279]
Nothing melted through the bottom of a steel reactor vessel at Fukushima. After accidents at Three Mile Island and Fukushima, fears of a “China syndrome” melt-through begin to seem unfounded. There is simply not enough heat generated by tons of hot fuel to make a hole in the bottom of a water-moderated reactor.
The workers at Fukushima I were dedicated to the tasks of bringing the reactors at the plant under control, with cold shutdowns a goal, and they worked without sleep, food, a way to get home, news from loved ones, or a remaining dwelling place, in a potentially dangerous radiation field. Two operators in the Unit 3 and 4 shared control room wore glasses, and their respirators would not fit correctly over their spectacles. Air containing radioactive dust leaked in to their breathing apparatus. One received a dose of 59 rem, and one received 64 rem. These were serious but not immediately fatal lung exposures. With workers retreating inside as the result of various explosions, the Emergency Response Center became heavily contaminated with radioactive dirt, and there were no controls in place to prevent radiation exposures. Workers who never worked near a reactor received substantial internal radiation doses. One woman, for example, received a dose of 1.35 rem.
As of September 1, 2013, there have been 10,095 aftershocks from the Tohoku earthquake of March 11, 2011.
With four nuclear power plants in a direct line of the tsunami waves following the Tohoku earthquake, what was it specifically about Fukushima I that caused it to be destroyed that made it different from other reactors? TEPCO, having ignored studies warning of a major earthquake and a tall tsunami, was widely blamed for the disaster. None of the preparations for a major off-shore earthquake were adequate, and the probability of an earthquake disaster, and the likelihood of a corollary tsunami, was not taken seriously. The nuclear regulatory structure in Japan as well as the prime minister himself were under fire for not having insisted on more rigorous safety inspections and preparations, but what caused this highly localized breakdown when seventeen other nuclear power plants around Japan were rattled in the same earthquake? Those plants located on the east coast were even hit with the same tsunami.
Consider the fate of Fukushima II, a nuclear power plant built by TEPCO, seven miles down the coast from Fukushima I. It is a newer power plant, having four General Electric BWR/5 reactors with Mark II containment structures, built under license by Toshiba and Hitachi. The reactors came online between 1981 and 1986, producing a combined 4.4 billion watts of electrical power. All four units were operating at full power on March 11, 2011, when the Tohoku earthquake struck Japan.
Immediately during the earthquake, all four units scrammed and automatically began emergency cool-down measures. Three out of four off-site power sources went down, and the emergency diesels started. A tsunami warning was issued, indicating that a wave at least 10 feet high was on its way. All operators were called to the control rooms, and everybody else was evacuated to high ground. In 36 minutes, the waves started coming. The highest in the area of the main buildings was 49 feet, and it swamped the 17.1-foot tsunami wall, covering the entire plant in seawater.
The tsunami knocked out the majority of emergency diesel generators and above-ground seawater pumps, but Unit 3 kept both its generators and its pumps, and Unit 4 still had one generator. The last remaining high-voltage electrical line out of the plant site after the earthquake remained operable. Using this off-site power and cross-connections with the three remaining diesels, all control-room instruments and controls remained in operation. All four reactors were depressurized, and coolant injection was established using the condensate water tanks, exactly as detailed in the written emergency procedures. Unit 1 required manual actuation of some motor-driven valves, but there was no radiation leakage or loss of lighting in the reactor building, and the workers were not dosed.
Unit 3 used its still-operational seawater pumps to achieve a cold shutdown, but Units 1, 2, and 4 used a spray of water from the condensation tanks to cool off the hot water pooled in the Mark II containment wet wells. New seawater pumps and a lot of temporary electrical cable were urgently needed, and TEPCO managed to find these supplies and lower them onto the plant site using helicopters the next day. About 200 workers, unimpeded by radiation contamination on the ground, installed the new motors and 5.6 miles of new electrical cable in 36 hours. By 3:42 P.M. on March 14, three days after the earthquake, all four units were being cooled using the seawater-driven Residual Heat Removal Systems, and the reactors were in cold shutdown on March 15.
The important differences between Fukushima I and Fukushima II seem to center on the ages of the two plants and the resulting differences in design sophistication. Nuclear-plant designs, all of which are experimental, rapidly evolved in the 1970s as lessons were learned and things that worked well were kept while things that did not work well were redesigned. The Mark II containment structure was a welcomed improvement and simplification of the much-debated Mark I.
Using air-cooled instead of seawater-cooled emergency diesel generators, located out of the basements and above ground, was also important. Being washed over by a wave was different from being soaked in a permanent pool of salt water, particularly if the engines used electrically driven pumps to circulate water out of the ocean, where the intakes were destroyed by the tsunami, and the electrical distribution boxes were left under water.
Fukushima II was also simply luckier than Fukushima I, which had its entire electrical switching yard wiped out, including the inter-unit electrical connections. Unit 1 at Fukushima I, having the smallest of the six reactors, had a lesser heat load to manage using the same Mark I containment structure that Units 1 and 3 had. Its set of two isolation condensers, unique to it at the plant, was ingenious and robust, and there was no reason why it could not have saved the reactor from destruction and brought it down to a cold shutdown without the convenience of emergency electrical power, if only it had not been turned off. The fate of Fukushima I, the safety reputation of American-designed light-water reactors, the remains of the nuclear power industry, and the background radiation in the Sendai Province could all have been different.
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The reactors would have survived, but the steam turbine rotors would have been ruined. A major job of the diesel backup generators is to keep the turbine turning, if even at a very slow speed, using the electrically driven “jacking gear.” A large steam turbine must be kept turning at all times. If allowed to sit still for a few hours, the rotors will sag, losing balance and rubbing against the metal shell that covers the turbine. In this distorted condition, the turbine cannot be restarted. The backup batteries will not maintain this essential service to the turbine.